This invention relates to a power supply voltage control apparatus.
Some electronic circuits using C-MOS devices are equipped with a special arrangement for protecting the C-MOS devices. Specifically, when the voltage of an input signal to a C-MOS device exceeds a power supply voltage, the protective arrangement leaks a current from an input signal line to a power supply line to prevent an excessive increase in the voltage of the input signal and thereby to protect the C-MOS device from the high input signal voltage.
Such a leak current tends to cause an unwanted increase in the power supply voltage. It is known to provide a Zener diode at a suitable location within the electronic circuit to prevent the unwanted increase in the power supply voltage.
As will be explained later, an electronic circuit equipped with a protective arrangement and a Zener diode tends to perform unexpected and undesirable operation under certain conditions.